Novel water insoluble (Na_xAg_2-x)MoO₄ (0 ≤ x ≤ 2) microwave dielectric ceramics with spinel structure sintered at 410 degrees

In the present work, a novel series of water insoluble ultra-low temperature firing (Na,Ag)₂MoO₄ microwave dielectrics were prepared via the traditional solid state reaction method. A spinel structured solid solution was formed in the full composition range in the (Na_xAg_2-x)MoO₄ (0 ≤ x ≤ 2). As x increased from 0 to 2.0, cell volume decreased linearly from 9.32 Å to 9.10 Å. Sintering behavior were described using a so-called 'bowing' effect and densification was achieved below 420 °C for 0.5 ≤ x ≤ 1.2 with grain size, 1 to 5 μm. Optimum microwave dielectric properties were obtained for (Na_1.2Ag_0.8)MoO₄ ceramics sintered at 410 °C with a permittivity ∼8.1, a microwave quality factor ∼44 800 GHz and the temperature coefficient of the resonant frequency ∼-82 ppm °C^-1 at 13.9 GHz. Silver within the solid solution inhibited hydrolyzation of ceramics and also reduced their sintering temperature. Compared with the sintering temperatures of traditional microwave dielectric ceramic (Al₂O₃, >1400 °C) and normal low temperature co-fired ceramics (<960 °C), this system will save lots of energy during processing and accelerate developments of sustainable electronic materials and devices.